In a typical seal assembly a seal element is retained by a seal housing. The seal element provides a sealing surface which in service may be exposed to a variety of forces acting on the seal which tend to move or distort the seal element. This movement or distortion may result in the seal failing to perform as intended either by permitting leakage across the seal or by allowing abrasive media to become embedded in the sealing surface, thus causing premature wearing of the seal element.
The forces acting on the seal may be caused by a pressure differential across the seal element, in which case the sealing surface will tend to move or distort laterally within the seal housing either so that the, sealing force exerted by the sealing surface against its abutting component is reduced or so that the seal element is “lifted” out of the seal housing by fluid which passes under pressure between the seal element and the seal housing. These effects becomes more problematic where there is a high constant or transient differential pressure across the seal.
It may be possible to counteract these effects by using springs or other biasing devices to provide additional sealing force to keep the sealing surface engaged with both the abutting component and with the seal housing. Unfortunately, however, the necessary spring force increases with the pressures exerted on both sides of the seal and with the differential pressure across the seal. If the spring force is too high the amount of deformation and compression of the seal element caused by the spring force may itself result in the seal element failing to perform as intended.
Where the seal is a dynamic seal, the forces may also result from movement of components associated with the seal or from relative movement between the sealing surface and components abutting the sealing surface. If the dynamic seal provides a seal between components that move axially relative to each other then the seal element may tend to move axially due to friction in the same direction as the component that abuts the sealing surface. If the dynamic seal provides a seal between components that rotate relative to each other then the seal element may tend to rotate due to friction in the same direction as the component that abuts the sealing surface.
Regardless of whether the movement or distortion of the seal element is caused by differential pressure or relative movement of components, it may be controlled by providing one or more engagement forces between the seal element and the seal housing during service which restrain the seal element against movement in the seal housing.
The engagement force or forces between the seal element and the seal housing during service may be achieved by permanently fixing the seal element in the seal housing by gluing or otherwise connecting the seal element with the seal housing. Unfortunately this option may result in higher fabrication costs by complicating the design of the seal and may also increase the difficulty of replacing seal elements as they become worn.
There is therefore a need for a seal assembly in which movement or distortion of the seal element can be limited by providing one or more engagement forces between the seal element and the seal housing during service without permanently fixing the seal element in the seal housing and without relying exclusively on springs or other external mechanisms for supplying an effective engagement force.